Bone reconstitution in a complete osteal-periosteal discontinuity in the mid-shaft of the radius of skeletally mature dogs is the experimental model. A defect of "critical length" would be one which, in skeletally mature dogs, would not be re-established by bone without internal fixation, or its length could just barely exceed that of a discontinuity that would routinely heal only if internal fixation were used. Exogenous hormones will be administered to half of these otherwise physiologically intact skeletally mature dogs after surgical creation of the "critical length" radial discontinuities and application of internal fixation. To compare rate of bone formation in those receiving the hormones with those not receiving the hormones. BIBLIOGRAPHIC REFERENCE: Robinson, R.A.: "Physicochemical Structure of Bone". In Clinical Orthopaedics and Related Research, Vol. 112, October 1975 (In Press) Publisher: J.B. Lippincott Co., Philadelphia, Pa. Editor: Marshall R. Urist.